The present invention relates to cam device for a pressure regulating valve which can reliably maintain a correct contact relationship between a cam surface and a roller.
In a hydraulic circuit incorporated with a planetary gearing of an automatic transmission gear box in order to effect engagement or disengagement of friction engaging means such as a brake or clutch mechanism, usually pressure regulating valves such as a throttle valve linked with an accelerator pedal, for instance, are employed. FIGS. 7 and 8 show an example of these valves. The pressure regulating valve 1 as of throttle valve shown in these drawings includes a plunger 3 urged by a pressure regulating spring 2. At one end of the plunger 3, a roller 5 is rotatably supported by the plunger 3 via a pin 4.
Further, a plate cam 8 is pivotably supported by a support axle 7 fixed to a stationary member by a bolt shaft 6. A cam surface 9 of this plate cam 8 is brought into contact with the outer periphery of the roller 5. A cam wire 10 is connected to the plate cam 8 with one end of the wire 10 fixed to the plate cam 8. The cam wire 10 moves back and forth, as shown by arrows in FIG. 8, according to the depression stroke of an accelerator pedal to pivot the plate cam 8 about the support axle 7, so that the roller 5 and the plunger 3 are reciprocably moved according to the profile of the cam surface 9 in order to controllably open or close one or more ports of the pressure regulating valve 1. Further, in FIG. 7, the reference numeral 11 denotes a return spring for the plate cam 8. FIG. 9 shows an example of the relationship between strokes of the plunger 3 and rotation angle of the plate cam 8, which indicates that the plunger 3 moves relatively rapidly with a steep gradient up to point a but gradually after point a.
In the conventional pressure regulating cam as described above, there exists a problem such that the roller 5 rotates through 90 degrees about the axis of the plunger 3, during operation, from a correct position, e.g., as shown in FIG. 7 to such a position as shown in FIG. 10, so that the roller 5 will not roll along the cam surface 9, thus resulting in a stoppage of the valve operation.